Disclosed herein are low reflection, flexible, transparent, laminate electrodes and methods of making and using such electrodes, e.g. as a flexible electrode component of touch panel membrane switches.
A modern, electronic input device is a touch panel which is a transparent input device mounted in front of a video display. A touch panel is composed of two planer electrodes, one on top (or in front) of the other and separated by a thin space. The base electrode is usually rigid while the top electrode is flexible. The flexible electrode is called the touch panel membrane and comprises a conductive surface on a flexible sheet. Small dots of plastic are printed on the base electrode to create the gap that separates the two electrodes. The air gap is maintained between the two electrodes until the outer, flexible electrode is pressed, at a point, against the base electrode. The electronics of the device then compute the spatial position where contact between the two electrodes was made. The input is then used, as the application requires.
The touch panel is mounted in front of a display, so both electrodes must be optically transmissive. As a general rule, the more transmissive the better. This is usually accomplished by fabricating the base electrode of plastic or glass that has been coated with a transparent conductive material. The flexible electrode is a sheet of flexible plastic that has also been coated with a transparent conductive material. The two conductive layers are placed face to face. Under the pressure of a finger or stylus the flexible electrode bends down between the dots and makes electrical contact with the base electrode.
Each air/surface interface in the display generates a reflection. These reflections degrade the image from the display. The touch panel membrane has two surface/air interfaces. The interface that faces the viewer is called the xe2x80x9cfrontxe2x80x9d surface of the touch panel. The conductive surface interface at the xe2x80x9cbackxe2x80x9d of the flexible sheet faces the air gap. Hereinafter these two sides are referred to as xe2x80x9cfrontxe2x80x9d and xe2x80x9cbackxe2x80x9d. Both ambient light and light from the display are reflected at these two interfaces. Light from the display is reflected away from viewer and ambient light is reflected to the viewer. These occurrences combine to alter the color of the display, decrease brightness, and reduce the contrast ratio. This is a degradation of display performance.
The touch panel membrane is a composite construction based on a flexible sheet of plastic. The back side of the sheet, that makes contact with the base electrode, must be conductive. A thin layer of a transparent inorganic or, more recently, polymeric material is applied to provide the conductivity.
The front side of the sheet is usually coated with a hard plastic layer to withstand the constant contact from fingers or a stylus. In industry these are so-called xe2x80x98hard coatsxe2x80x99. For added durability the front and back sides of the substrate can be coated with hard coats.
This invention provides low reflective, transparent laminates which are useful as touch panel membrane electrodes. One aspect of the invention presented here is a touch panel membrane electrode that is both low reflecting and highly transmitting in the visible region. By reducing the light that is reflected from one or both surfaces of the flexible electrode, the view of the display is substantially improved. In addition, the laminate can be used for the base electrode, e.g. laminated onto a glass CRT screen. This reduces the reflection from where the base electrode meets the air gap.
The present invention restores the color, brightness and contrast to the display by modifying the front and/or back side of the membrane, using :thin-film anti-reflective layer(s). For best results both sides of the film can have anti-reflecting layers, and the base electrode can also have an anti-reflective layer. In addition to the use of anti-reflective thin films, the hard coats themselves may be physically modified to scatter some of the ambient light, reducing the reflection seen by the viewer even more.
In an aspect of the invention there is provided a flexible, transparent laminate adapted for use as an anti-reflective, membrane electrode. Such laminate is preferably manufactured in a continuous web comprising (a) a sheet of flexible, plastic substrate, (b) a conductive outer layer on one side of the substrate sheet, and (c) an anti-reflective stack of at least one pair of oxide layers on at least one of the sides of the substrate sheet. The laminate can be provided in wound rolls of continuous web.
The present invention may be embodied in three different ways. In every embodiment the touch panel membrane has a sheet of plastic film as a substrate. This plastic film is light transmissive, at least 60%, in the visible light range of 400 to 750 nanometers (nm), more preferably at least 80%, transmissive or higher, even more preferably at least 90% transmissive in the visible light range of 460 to 700 nm. The plastic film may be coated, on one side or both, with a scratch resistant layer. This layer may have a smooth surface or be textured to provide anti-glare properties. The hard layer(s) may be composed of a single material or layers of different materials. Each material may be organic or inorganic, homogeneous or contain particulate.
The first embodiment of the invention incorporates an anti-reflective thin film stack on the front of the membrane. The layer stack is applied to the front surface, on top of a hard layer, if present. The anti-reflective thin film stack may consist of one to 10 or more layers. One or more of the layers may be electrically conductive, e.g. to reduce static charge. The layers may be deposited by vacuum process or from a gas or liquid. The anti-reflective thin-film stack reduces the reflection to an average of 2% or lower between 400 and 700 nm. The top layer of the anti-reflective thin-film stack may be a low surface-energy, anti-finger print material. The back side of the film has only a transparent conductive coating. This layer may consist of one or more layers.
The second embodiment of the invention incorporates an anti-reflective thin film stack on the back of the sheet. The layer stack is applied to the back side on top of the hard layer but under the conductive layer. The anti-reflective, thin-film stack is composed of one to 10 or more layers. One or more of the layers may be conductive. The layers may be deposited by vacuum process or from a gas or liquid. The anti-reflective thin-film stack reduces the reflection of the conductive layer to an: average of 5 or less, between 400 and 700 nm. The front side of the film has only a hard layer.
This construction may also be used for the base electrode of the touch panel or pen entry device. The film can be laminated to a rigid, transparent substrate with the conductive layer facing the air gap. Having the anti-reflective thin film stack under the base electrode serves to improve the view of the display even more.
The third embodiment of the invention incorporates anti-reflective, thin film stacks on both the front and back sides of the sheet. One layer stack is applied to the front side, on top of the hard layer, if present. A second layer stack is applied to the back side, on top of the any hard layer but under the conductive layer. The anti-reflective, thin-film stacks are composed of one to 10 or more layers. One or more of the layers may be conductive. The layers may be deposited by vacuum process or from a gas or liquid. The anti-reflective, thin-film stack on the front reduces the reflection to an average of 2 or lower between 400 and 700 nm. The top layer on the anti-reflective thin-film stack may be a low surface-energy, anti-finger print material. On the back, the anti-reflective thin-film stack reduces the reflection of the conductive layer to an average of 5 or less, between 400 and 700 nm.
This invention also provides improvements in devices where data is entered by pressure activation on the surface of a display screen having a membrane electrode surface. The improvements arise from the use of an anti-reflective, conductive sheet in the electrode assembly.